Network providers are interested in providing centralized network services to meet customer demands. By taking advantage of the latest advances in IP quality of service (“QoS”), multiprotocol label switching (“MPLS”), and service transformation technology (the conversion of non-IP services to IP), service providers can evolve dedicated IP infrastructures into a multi-service network architecture, as an alternative to operating separate service-specific networks.
MPLS is a standards-approved technology for speeding up network traffic flow and making it easier to manage. MPLS involves setting up a specific path for a given sequence of packets, identified by a label put in each packet, thereby saving the time needed for a router to look up the address to the next node. MPLS is called multiprotocol because it works with the Internet Protocol (“IP”), Asynchronous Transport Mode (“ATM”), and various frame relay network protocols. MPLS allows most packets to be forwarded at the layer 2 (switching) level of the standard Open Systems Interconnection (“OSI”) rather than at the layer 3 (routing) level. In addition to moving traffic faster overall, MPLS makes it easy to manage a network for quality of service (“QoS”). For these reasons, the technique is expected to be readily adopted as networks begin to carry more and different mixtures of traffic.
The essence of MPLS is the generation of a short fixed-length “label” that acts as a shorthand representation of an IP packet's header and the use of that label to make forwarding decisions about the packet. Typically, IP data packets are routed from source to destination through a series of routers which receive the IP data packet, read the source and/or destination addresses and re-transmit the IP data packet either to the destination indicated as indicated by the IP destination addressed contained in the IP data packet or to another router which will forward the IP data packet until the IP data packet reaches the destination address, referred to as hop by hop routing. IP packet headers have fields for IP source and/or destination addresses. Routing protocols such as Routing Information Protocol (“RIP”) and Open Shortest Path First (“OSPF”) enable each machine to understand which other machine in the “next hop” that a packet should take toward its destination.
In MPLS, the IP packets are encapsulated with labels by the first MPLS device they encounter as they enter the network. The MPLS edge router analyses the contents of the IP header and selects an appropriate label with which to encapsulate the packet. In contrast to conventional IP routing, the router analysis can be based on more than just the destination address carried in the IP header. At all the subsequent nodes within the network the MPLS label, and not the IP header, is used to make the forwarding decision for the packet. As MPLS labeled packets leave the network, another edge router removes the labels. In MPLS terminology, the packet handling nodes or routers are called Label Switched Routers (LSRs). MPLS routers forward packets by making switching decisions based on the MPLS label. There are two broad categories of LSR: MPLS edge routers, which are high performance packet classifiers that apply (and remove) the requisite label at the edge of the network; and Core LSRs which are capable of processing the labeled packets at extremely high bandwidths.
Traditional routing solutions for efficient use of IP addressing have included using a content addressable memory (CAM) device for storing IP addresses. A CAM is a storage device that can be instructed to compare a specific pattern of comparand data with data stored in its associative CAM array. The entire CAM array, or segments thereof, are searched in parallel for a match with the comparand data. If a match exists, the CAM device indicates the match by asserting a match flag. Multiple matches may also be indicated by asserting a multiple match flag. The CAM device typically includes a priority encoder to translate the highest priority matching location into a match address or CAM index. The generally fast parallel search capabilities of CAMs have proven useful in many applications including address filtering and lookups in routers and networking equipment, policy enforcement in policy-based routers, pattern recognition for encryption/decryption and compression/decompression applications, and other pattern recognition applications.
Binary CAM cells are able to store two states of information: a logic one state and a logic zero state. Binary CAM cells typically include a RAM cell and a compare circuit. The compare circuit compares the comparand data with data stored in the RAM cell and drives a match line to a predetermined state when there is a match. Columns of binary CAM cells may be globally masked by mask data stored in one or more global mask registers. Ternary CAM cells are mask-per-bit CAM cells that effectively store three states of information, namely: a logic one state, a logic zero state, and a don't care state for compare operations. Ternary CAM cells typically include a second RAM cell that stores local mask data for the each ternary CAM cell. The local mask data masks the comparison result of the comparand data with the data stored in the first RAM cell such that the comparison result does not affect the match line. The ternary CAM cell offers more flexibility to the user to determine on an entry-per-entry basis which bits in a word will be masked during a compare operation.
U.S. Pat. No. 6,237,061 describes a system in which Classless Inter-Domain Routing (CIDR) addresses are pre-sorted and loaded into the ternary CAM such that the CAM entry having the longest prefix is located at the highest numerical address or index. The prefix portions of the CIDR addresses are used to set the masks cells associated with each CAM entry such that during compare operations, only the unmasked prefix portion of each CAM entry, which may correspond to a network ID field, is compared to an incoming destination address stored as the CAM search key. Since each CAM entry is masked according to an associated prefix value, the ternary CAM requires only one search operation to locate the CAM entry having the longest matching prefix.
Some other network services which are offered by network providers include Internet Protocol (IP) Virtual Private Networks (VPN) to interconnect various customer sites that are geographically dispersed. VPNs offer privacy and cost efficiency through network infrastructure sharing. U.S. Pat. No. 6,205,488 describes a virtual private network including multiple routers connected to a shared MPLS network which are configured to dynamically distribute VPN information across the shared MPLS network.
Policy-based routing services have also been described to allow customers to implement policies that selectively cause packets to take different paths. Conventional applications of policy based routing have included: source based transit provider selection for routing traffic originating from different sets of users through different Internet connections across the policy routers; quality of service (QOS) for prioritizing traffic based on the type of service; and cost savings for distributing traffic between low-bandwidth, low cost permanent paths and high-bandwidth, high cost, switched paths.
It is desirable to provide a method and system having fast search capabilities through use of a TCAM for classifying a plurality of types of data traffic and route lookup.